1. Technical Field
The disclosure of the present application relates generally to the treatment of turbine blades to increase their hardness and/or durability.
2. Background
The aviation and/or industrial gas turbine engine is comprised of a series of rotating and stationary airfoil components arranged in stages. These components are grouped in two areas of the engine: the compressor, or ‘cold’ section, and the turbine, or ‘hot’ section. Air, drawn into the forward cold section is compressed as it passes over the airfoils and is forced into the hot section in which fuel is injected and combustion occurs. As a result of that combustion, the hot expanding gas is forced over and through the rear turbine blades and vanes, which in turn, accelerates the rotation of the compressor blades to increase fuel combustion with a corresponding increase in thrust or available energy.
A substantial amount of the energy developed from the fuel combustion is dedicated to running the compressor section of the turbine. The excess energy from driving the compressor becomes either thrust to push the engine if attached to an airplane or rotational energy in ground based applications.
Over time, erosion caused by airborne particles and pollutants wears the airfoils of the turbine, resulting in gradual loss of cross-section and airfoil thickness. To compensate for cross-section loss and subsequent deterioration of the aerodynamics of the compressor blades, more fuel is consumed to maintain the required energy output.
A thin layer of hard wear-resistant coating can maintain efficiency for a longer period of time and result in considerable fuel cost savings over the life of the engine. Even a 1% increase in fuel efficiency represents significant fuel cost savings. For example, in terms of 2005 fuel consumption data, as much as $460,000,000 of fuel cost savings per year to all US carriers combined can be realized for each 1% increase in fuel efficiency (Air Transport Association Economics and Energy Bulletin, Jan. 18, 2007).
Treating metallic components with boron is one way to improve wear resistance; however, some boron treatments result in surfaces that are brittle and crack easily. One method developed to provide a surface resistant to cracking or deformation was disclosed in U.S. Pat. Nos. 3,842,921 and 3,922,038, which are incorporated herein by reference. These patents teach a method of carburizing surfaces prone to wear, boronizing the carburized surfaces, and then tempering the resulting boronized surfaces. In both patents, the treatment was applied to earth boring drill bits, prone to abrasive wear when in use. A number of other patents teach processes for creating a corrosion resistant coating of different types of metals, including U.S. Pat. Nos. 3,024,175; 3,024,176; 3,024,177; RE 25,630; and 3,479,159, all are incorporated herein by reference.
Boron has been previously used as an element of turbine blades, particularly at the tip of the blade, as taught by U.S. Pat. No. 5,573,604, which is incorporated herein by reference, where a portion of titanium turbine blades at the tip of the blade are alloyed with carbon, nitrogen, or boron, to increase the durability of that portion of the blade. Application of boron to the entire turbine blade will improve the hardness and/or durability over the entire body of the turbine blade, increasing the useful life of the component as a whole.